Unit 15- Earth’s History

The Geologic Time Scale Structure of the Time Scale  Based on their interpretations of the rock record, geologists have divided Earth’s 4.56-billion-year history into units that represent specific amounts of time. Taken together, these time spans make up the geologic time scale.

The Geologic Time Scale Structure of the Time Scale Eons represent the greatest expanses of time. Eons are divided into eras. Each era is subdivided into periods. Finally, periods are divided into smaller units called epochs. Phaneroic-derived from Greek meaning “visible life”  There are three eras within the Phanerozoic eon: the Paleozoic, which means “ancient life,” the Mesozoic, which means “middle life,” and the Cenozoic, which means “recent life.”

The Geologic Time Scale Structure of the Time Scale  Each period within an era is characterized by somewhat less profound changes in life forms as compared with the changes that occur during an era.  The periods of the Cenozoic era are divided into still smaller units called epochs, during which even less profound changes in life forms occur.

12.4 The Geologic Time Scale Precambrian Time Precambrian time-540 mya Represents 88% of earth’s time history During Precambrian time, there were fewer life forms. These life forms are more difficult to identify and the rocks have been disturbed often. Three eons within this time: starting from most recent-Proterzoic, Archean, Hadean

The Geologic Time Scale Makes no sense without caption in book

Precambrian Time: Vast and Puzzling Encompasses the most geologic time from about 4.56 billion years ago until the start of the Cambrian period, 4 billion years later. All time between origin of earth and 570 mya

Precambrian Time Most Precambrian rocks do not contain fossils Much of what we know about Precambrian rocks comes from ores mined from shields Shields-large relatively, flat expanses of ancient metamorphic rock within the stable continental interior Ex.-iron, nickel, gold, silver, copper, chromium, uranium, and diamond mines have provided samples Oldest Rocks/Fossils-Stromatolites

Precambrian Rocks

Earth’s Atmosphere Evolves Earth’s original atmosphere was made up of gases similar to those released in volcanic eruptions today– water vapor, carbon dioxide, nitrogen, and several trace gases but NO oxygen Later, primary plants evolved that used photosynthesis and released oxygen At first, most oxygen combined with iron to make rust Oxygen began to accumulate about 2.5 bya

Precambrian Fossils The most common Precambrian Fossils are Stromatolites Stromatolites are distinctively layered mounds or columns of calcium carbonate. They are NOT the remains of actual organisms but are the material deposited by aglae They did not become common until the middle of the Precambrian time, about 2 bya. Many of these ancient fossils are preserved in chert-a hard dens chemical sedimentary rock

Paleozoic Era: Life Explodes

The Paleozoic era encompasses about 292 million years Following the long Precambrian time, the most recent 540 million years of Earth’s History are divided into three eras: Paleozoic Mesozoic Cenozoic The Paleozoic era encompasses about 292 million years Before the Paleozoic, life forms possessed NO hard parts like shells, scales, bones, or teeth Paleozoic contains many more diverse fossils due to the emergence of life forms with hard parts

Paleozoic is divided into Early Paleozoic (Carmbrian, Ordovician, Silurian periods) & Late Paleozoic (Devonian, Mississippian, Pennsylvanian, Permian periods)

Early Paleozoic History Consists of 123 million year time span that includes Cambrian, Ordovician, and Silurian periods During this time, the vast southern continent of Gondwana encompassed 5 continents (South America, Africa, Australia, Antarctica, and part of Asia)

Early Paleozoic Life Early Paleozoic Life was restricted to the seas No vertebrates had evolved so all were invertebrates Beginning of Cambrian time-1st animals with hard parts like shells for protection and adaptation By Cambrian time-Trilobites By Ordovician times-Brachiopods & Cephalopods Cephalopod-mobile and most developed mollusks; were big predators 1st large organism on earth

Life in the Ordovician Period

Late Paleozoic History Spans about 160 million years Includes Devonian, Mississippian, Pennsylvanian, and Permian Laurasia is the continental mass that formed the northern portion of Pangea, consisting of the present-day North America and Eurasia As Laurasia was forming, Gondwana moved northward By the end of the Paleozoic, all of the continents had fused into the supercontinent of Pangaea Changed climate drastically. Most of the interior became arid.

Late Paleozoic Life During this time, organisms diversified dramatically Some 400 million years ago, plants that had adapted to survive at the water’s edge began moving inland, becoming land plants Earliest land plants were about the size of index finger, by end of paleozoic, had forests with trees tens of meters high Ocean life developed more light-weight scales During Devonian-primative sharks Devonian age-”Life of the Fishes”

Late Paleozoic Life By end of Devonian period, amphibians started to emerge The amphibians rapidly developed and diversified because they had minimal competition from other land dwellers By the end of the Pennsylvanian period, large tropical swamps extended across North America, Europe, and Siberia Coal deposits originated in these swamps 1st Reptiles appeared

The Great Paleozoic Extinction The world’s climate became very seasonal probably causing the dramatic extinction of many species During Permian period-Pangaea The late Paleozoic extinction was the greatest of at least five mass extinctions over the past 500 million years By end of Permian, 75 species of amphibians gone, at least 80% of marine life gone,

The Great Paleozoic Extinction Cause is uncertain- Sea levels had dropped because of climates Climate changes from Pangaea At least 2 million cubic yards of lava flowed across Siberia May have been from impact from extraterrestrial body

The Mesozoic Era: Age of the Reptiles

Mesozoic Era Spanned about 183 million years Divided into three periods Triassic Jurassic Cretaceous Beginning of the breakup of Pangaea continued for 200 million years through the Mesozoic and into the Cenozoic era Dinosaurs became dominant and remained unchallenged for over 100 million years

Mesozoic History Began with most of worlds land above sea level; then shallow seas invaded much of western North America, the Atlantic, and Gulf coastal regions These shallow seas created great swamps like those of the Paleozoic era forming Cretaceous coal deposits that are important in Western US and Canada As Pangaea broke apart, North American plate began to override Pacific Plate. Lead to forming mountains of Western US. By end of Mesozoic, Rockies began to form

Mesozoic Life When era began, life forms were the survivors of great extinction in Paleozoic era. The gymnosperms are seed-bearing plants that do not depend on free-standing water for fertilization Quickly became dominate plants of the era Ex-confers, ginkgoes trees

Mesozoic Life The shelled egg Unlike amphibians, reptiles have shell-covered eggs that can be laid on the land The elimination of a water dwelling stage was an important evolutionary stage

Mesozoic Life Because of the shelled egg, reptiles quickly became the dominant land animals Some dinosaurs were carnivores (meat-eaters) some were herbivores (plant-eaters) Not all dinosaurs were large Some began to fly Some returned to the sea By end of the Mesozoic era-many reptile groups became extinct

Mesozoic Life After extinction only a few reptiles survived to recent times-turtles, snakes, crocodiles, lizards Extinction of dinosaurs and other animals most likely caused by a large meterorite that collided with Earth They think the impact created large quantities of dust that blocked out the sun Without the sun, plants died, then herbivores died, then carnivores died.

The Cenozoic Era-Age of Mammals

Cenozoic Era Cenozoic Era-”era of recent life” Encompasses past 65 million years Post-dinosaur era, the time of mammals, including humans (Quaternary) Divided into to periods of very unequal duration, the Tertiary period (63 million years) and the Quaternary Period (last 2 million years)

Cenozoic North America Plate interactions during the Cenozoic era caused many events of mountain building, volcanism, and earthquakes in the West The Atlantic and Gulf coastal regions were far removed from an active plate boundary, so they were stable

Cenozoic Life Even though Cenozoic is called age of mammals, could also be age of Angiosperms Angiosperms-flowering plants with covered seeds-replaced gymnosperms as dominant land plants Influenced evolution of birds and mammals

Cenozoic Life Mammals replaced reptiles as the dominant land animals Mammals bear live young and maintain steady body temperature Even though mammals and dinosaurs emerged at the same time in the late Triassic period, mammals remained small and primitive Adaptations like being warm-blooded (could search for food during any season or time of day), developing insulating body hair, and having more efficient heart and lungs allow mammals to lead more active lives than reptiles

Large Mammals and Extinction Some groups of mammals became very large Many were common up to 11,000 years ago However, a wave of late Pleistocene extinctions rapidly eliminated these animals from the landscape (during the last Ice Age) In North America, the mastodon and mammoth both relatives of the elephant became extinct Cause of recent extinction debatable…..

Some think it is because of the last ice age BUT-the animals had survived other glacial advances and intergalical periods Some scientists believe that the early humans hurried the decline of these mammals by selectively hunting large forms Humans first appear in the Quaternary Period

NM Geologic History Rocks from each of the four eras can be found within the state

NM Geologic History Precambrian igneous and metamorphic rocks of more than 1.5 billion years old have been found These rocks form the core of mountain ranges along the east side of the Rio Grande River Oldest of the Precambrian rocks found in northern part of state in the Brazos, Taos, and Nacimiento mountains dating 1.8 billion years old Most likely have been buried and later exposed by the uplift of mountain chains and erosion of sediments During Precambrian=-NM had volcanic activity, mountain building, periodic episodes of submersion under the sea Only remnants of these old mountain systems remain

Paleozoic Era During later part of Paleozoic, Rocky Mountains formed, uplifting the central part of the state Toward southern part of NM, a great barrier reef developed. As the reef was cut off from the sea, the evaporation of water left deposits of salt, potash, and gypsum that can be found today State was covered by vast shallow sea, from which large deposits of limestone, sandstone, and shale accumulated

Mesozoic Era Drying trend Dinosaurs roamed much of the state Many of the rocks of the northern part of the state including the colorful red, green, gray, brown, and white sandstone and shale were deposited by rivers that flowed towards the seas Later in the era, the inland sea once again returned and NM was on the western shore of a great shallow ocean covering most of the central US

Cenozoic Within the last 10 million years, NM has seen tremendous volcanic eruptions, such as those that produced the Jemez Mountains, Capullin Peak, and Mt. Taylor The continuous erosion and deposition of sediments in recent times have produced many of the more scenic landscapes of the state, such as its colorful mesas, badlands, and deserts Much change in NM landscape Rocky Mountains rose and volcanoes produced a thick layer of igneous rock that covered much of NM Shiprock was formed about 25 million years ago In addition, stresses in the crust produced the large central depression that divides the state in half, called the Rio Grande rift